The various metal subgenres definitely get their fair, and unfair, share of sand kicked in their faces.
But picture Grunge...Stone Temple Pilots and Soundgarden weren't really all that different from each other.
(Come at me, Grungebunnies.)
When metal is considered (Fight me, Kim Thayil!), the lines that delineate what is and is not metal are far more blurred. Is Deep Purple metal?
Zeppelin? Sabbath? What about Kiss?
Then when you get into what individual metal fans like. There are folks I know that are as metal as the day is long on the Summer Solstice, but wouldn't ever consider listening to Carcass, Mayhem, or Fisthammer.